my namie is lalalal... lalala...
>> nice name :-)
I com from Poland.
>> come
I am eighteen years old.
I learn in the three alass secondary school.
>> I am a student of a third class at secondary school
or I am learning at secondary school, in a third class.
I am writind in taking part in summer englisch course.
>> writing, ale to zdanie jest niepoprawne
moze byc np.
I am writing to you, because I am interested in your English summer course.
I would like to know more when this course is starting?
>> I would like to get to know/to be informed when does this course start?
I would like to know jest jakby mniej formalne. Jak piszesz do instytucji, to trzeba sie wysilic :-)